In prior art, there was used a contact type position sensor having a resistive element and a brush slipping on the resistive element, as the position sensor used in the EGR control valve. Recently, it has been required that such a position sensor is used under severer working circumstances or for years.
Against such requirements, however, the contact type position sensor has possibilities of occurrence of silicon compounds due to irruption of siloxane gas, sticking of abrasion powder caused by the brush acting minutely at high-G frequencies, or obstructed positional detection due to increasing of contact resistance caused by the sticking of abrasion powder on a contact area of the brush.
Additionally, as the brush slides on a resistant layer, abrasion of a sliding area is unavoidable, so that there is a limit in the number of operations of the sensor.
Therefore, according to the conventional contact type position sensor, it is difficult to meet the above requirements.
In this view, the need of employing a non-contact type position sensor having no contact area has been increased.
As the non-contact sensor like this, a sensor using a hall sensor has been developed. Thus, there are one sensor that utilizes a magnet formed with one pole in a moving direction and further uses, as a magnetic path, a gap of a stator where the magnet moves as described in Japanese Patent Publication No. 3264929, and another sensor that utilizes a magnet formed with two poles (N, S) in a moving direction and arranges a stator so to oppose one side of the magnet as described in Japanese Patent Laid-Open No. 2001-74409.